1. Field of the Invention
This invention relates generally to power supplies and more particularly, but not by way of limitation, to reserve power supplies for providing a backup to primary power supplies in computer systems.
2. Description of the Prior Art
One consideration which must be provided for in the utilization of electronic computers is the preservation of information when a power flicker, brownout, or outage occurs in the primary power supply of the computer system. To enable the computer to retain the information by transferring it to some type of permanent storage device during such a power failure, it is desirable to augment the primary power supply with a reserve power supply.
To provide a reserve power supply which is reliable enough to energize the computer for a sufficient time period during which the computer may effect necessary information transfers, it is necessary for the reserve power supply to be rechargeable during its operating mode so that it is retained in an electrically charged condition while it is standing by in readiness to power the computer when the primary power supply goes down. Furthermore, it is desirable that the reserve power supply be rechargeable at a faster rate when it is not in such a standby mode. Additionally, it is desirable for the reserve power supply to include means whereby the reserve supply may be disconnected from the primary power supply and the computer.
To reduce the chances of malfunctions and to improve the ease with which the power supply may be maintained, it is desirable that the reserve power supply have a simple construction and be easy to install. By having the features of simple construction and ease of installation, the reserve power supply can also be relatively economical as compared to more complex reserve power supplies.
So that the operator of the computer will know when the reserve power supply is standing by or when it is providing power to the computer, it is necessary to include means within the reserve power supply whereby audible and/or visual signals can be generated. Furthermore, there is the need to provide a plurality of voltage levels to the computer system when the primary supply fails.
That there is such a need for reserve power supplies is generally indicated in U.S. Pat. No. 4,143,283 in the name of Graf et al. This patent discloses a backup system which switches a bank of batteries from a series connection to a parallel connection a short time after the primary power supply fails. The batteries are connected in parallel to power the random access memories of the computer system within which the battery backup system is used.
Although the Graf et al. patent discloses one type of reserve power supply thereby indicating the need for such apparatus, I do not believe that it discloses a reserve power supply exhibiting the features of one constructed according to my invention as hereinbelow described. In particular, I believe that previously constructed or proposed devices have the shortcoming of failing to provide a relatively simply constructed reserve power supply which is simple to install and maintain, and is therefore relatively economical, and which provides backup power for all voltage levels needed by a computer to transfer necessary information to a permanent storage device, and also which can be operated and recharged in a standby mode with the batteries of the reserve power supply connected in series or can be more quickly recharged in a charge only mode with the batteries connected in parallel.